Microwave cooking is now an accepted method of preparing foods with approximately 50% of the U.S. households having a microwave oven.
The typical microwave oven does not confine moisture but instead readily, and in most cases forcibly, circulates air through and away from the oven cavity. Because of the forced circulation and due to the cavity area being relatively large as compared with the food or other material being heated, a large percentage of the moisture contained in the heated material is lost to the surrounding atmosphere.
Most foods have a critical moisture content required for edibility, thus it is especially desirable that the moisture given off from the heated product not drip back into the food since it renders the food soggy or collects in the base of the container, which can spoil the product by changing its consistency and palatability.
Various products have been devised for covering the dish during cooking or reheating of foods within microwave ovens. The propensity of food when heated to give off hot vapors such as steam has long been recognized. U.S. Pat. No. 3,955,710 teaches the use of a foam polystyrene cover of dish form which, when inverted and coupled to an underlying dish functions to maintain the hot food hot for a significant period of time. In such a cover, apertures provide vent openings to allow for the escape of hot vapors such as steam, which may be given off when the hot food items are enclosed by such covers.
U.S. Pat. No. 4,495,392 teaches microwave cooking systems consisting of a thermally insulated holder for foods having a thermally reflective shield for reflecting thermal radiation from the food to thereby reduce loss of heat by radiation through the thermal insulation layer while providing for the propagation of microwave energy into the food through the thermal insulating portion of the food holder. Specifically a container is provided with thick walls of low microwave loss material such as alundum having portions of the inside or outside of the container coated with a layer which reflects radiated infrared energy back into the food.
U.S. Pat. No. 4,705,927 teaches a microwave oven cooking utensil utilizing a water absorbing member underlying a microwave opaque cooking container with the container covered by a microwave transparent top. Water in the saturated absorbent pad is quickly heated by microwave exposure and converted to steam which contacts the exterior surfaces of the bottom and side wall of the container to facilitate thawing of the food (frozen) within the dish.
U.S. Pat. No. 4,721,140 teaches a flat, rectangular plan configured cover for placement across the open top of a dish with the edge of the cover overlapping the edge of the dish. The cover is preferably formed as a sheet of open weave material such as polyester and includes weights at the corners for holding the cover in place to prevent food spattering during heating of foods therein.
U.S. Pat. No. 4,797,523 teaches a cellulose hydrate film which is microwave transparent applied by stretching the same across the open top of a bowl or dish and having a plurality of ventilation holes therein. The film is dried when heated by microwave radiation and stretches over the container opening. The air expanding within the container may escape through the ventilation holes.
U.S. Pat. No. 4,801,773 teaches a cover with a flat top and tapered sides of oval, rectangular or circular top configuration, formed of light weight, moisture absorbent material which is readily disposable and which functions to eliminate extensive soiling of the interior of the oven by preventing food spattering.
While the shrouds or covers of the prior art, as exemplified by the patents above, function to produce certain beneficial effects, limited to spattering prevention, release of moisture from the chamber formed by the shroud or cover and the dish, the patents are devoid of the recognition of the need for critical moisture content of the food being heated or cooked, the necessity to prevent moisture dripping back into the food and need for release of excess moisture where necessary from the chamber defined by the cover and dish while providing a cover which is of low cost, low mass and which is readily disposable. For instance, the applicants discovered that if one merely inverts a bowl on a plate of food to be heated in a microwave oven, the moisture evolving from the food and condensing on the inner wall of the bowl will particularly drip back onto the food from the flat bottom of the bowl and further, where the inner wall is downwardly and outwardly inclined, will flow by gravity onto the food about the periphery of the dish supporting the upended bowl.
It is therefore a primary object of the present invention to provide a disposable food cover for covering a plate of food during heating or cooking within a microwave oven, which is formed of a moisture resistant material to minimize absorption of the moisture removed from the food during cooking or heating, which is structurally reinforced to provide structural strength, which facilitates the collection of condensate and traps the same for revaporization, which automatically permits the escape of excessive moisture, which is highly disposable, easily crushed and preferably biodegradable, which enhances stackability of the covers, and which has sufficient insulative property to retain heat during and after the time of food preparation, and which is of low cost.